A person skilled in the art knows a variety of methods for changing the color of human hair. In general, either substantive dyes or oxidation dyes are used to dye human hair, which are created by oxidatively coupling one or more developer components among one another or to one or more coupler components. The coupler and developer components are also referred to as oxidation dye precursors. The colorations achieved with oxidation dyes are typically referred to as permanent or semi-permanent colorations.
These agents usually comprise hydrogen peroxide as the oxidizing agent. Since hydrogen peroxide is only insufficiently storage-stable in the alkaline pH range, oxidative dyes are usually composed of two components, which are mixed with one another immediately before being applied. The one component comprises hydrogen peroxide in an aqueous solution or emulsion, wherein this composition has an acid pH value in the range of 3 to 5.5 to stabilize the hydrogen peroxide. The second component includes the dye precursors and one or more alkalizing agents in an amount such that the application mixture composed of the two components has a pH value in the range of 8 to 11. In addition, dyeing kits and dyeing methods are available, in which the application mixture composed of the two components has a pH value in the range of approximately 6 to 7.9; the coloring result of these so-called “acid” colorations, however, frequently do not achieve the quality attained with alkaline application mixtures.
The dye component is usually present in the form of an emulsion or gel of approximately 20 to 85 wt. %. However, dyeing kits in which the dye component is present in powdered form are also available. Advantages of these powders are that the oxidation dye precursors are present in solid form, and not in solute form, and consequently do not have to be stabilized to the same degree as dyeing emulsions or dyeing gels to prevent premature oxidation. Dyeing powders are also technologically less complex and less expensive to produce than dyeing emulsions and gels.
Powdered oxidation dye precursors can clump during extended storage, which makes it more difficult to produce a homogeneous application mixture from the powder and the aqueous oxidizing agent preparation. For this reason, a flow aid or an anti-caking agent is typically added to the dye powders, which itself is not water-soluble, such as silica. In addition, dyeing kits comprising dye powders and oxidizing agent preparations are available in the market, in which the dye powder comprises insoluble pigments that approximately reflect the color effect of the permanent hair color that is achieved. To oxidatively dye hair, the dye powder is mixed with an aqueous oxidizing agent preparation, for example in a bottle or a shaker cap, and the resulting cream-like application mixture is applied to the hair to be dyed, where it remains for a residence time of 5 to 60 minutes before being rinsed off again.
These products can be subject to the drawback that the application mixture, which represents a dispersion of the insoluble powder components in the aqueous oxidizing agent preparation, separates into solid and liquid components already before the recommended residence time has lapsed, thereby losing viscosity and dripping off the hair.
It is therefore desirable to provide an improved oxidizing agent preparation for oxidative dyes made of dye powders and oxidizing agents, which allows stable powder dispersions to be produced that have sufficient viscosity during the entire residence time and remain on the hair without dripping off. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.